Temporal analysis of the infiltration dynamics of pro-inflammatory cytokine-producing innate and adaptive immune cells following experimental traumatic brain injury in mice

Traumatic brain injury (TBI) is the leading cause of death and disability in young adults. A key factor in the aftermath of TBI is the response to pro-inflammatory cytokines such as interleukin(IL)-1β (IL-1β), tumor necrosis factor (TNF-α), IL-6, IL-17, and interferon-γ (IFNγ). This preclinical study examined key cytokine-producing cells post-TBI in mice.Adult C57BL/6J male mice underwent controlled cortical impact or sham surgery. Mice were euthanized, and brains harvested acutely at 3 hours (h), 6h, 12h, 24h post-injury, or subacutely at 3, 10, and 28 days post-injury (DPI). Mononuclear cells were obtained by percoll density gradient and FACS stained to identify infiltrating immune cells in the brain (Neutrophils, Monocytes, Dendritic cells, T-cell subsets (CD4+, CD8+, TCRγδ+)), as well as levels of intracellular cytokines.Following TBI, neutrophils rapidly infiltrated at 3h post-injury, with monocytes and dendritic cells following at 6h post-injury; all infiltrating innate immune cells produced IL-1β, IL-6, TNF-α. In contrast, T-cell infiltration peaked at 10 DPI and persisted through 28 DPI. Notably, IL-17 production was observed at 3 DPI and peaked at 10 DPI, and was mainly produced by γδ T cells. IFN-γ was produced by CD4+, CD8+ T cells, which peaked at 10 DPI.In summary, this temporal analysis revealed that IL-1β, IL-6, and TNF-α are primarily produced by innate immune cells in the acute phase post-injury, whereas IL-17 was produced by γδ T cells, and IFN-γ by CD4+ and CD8+ T cells at chronic timepoints. This study identifies infiltrating pro-inflammatory cytokine cellular targets for therapeutic intervention post-TBI.